Worth noting is that our students made all the tech driving the game. So the engine was developed along with the game by the team.
So one of the reasons they can keep the size relatively small is because there isn't a lot of clutter in the files. :)
If it was made in unity or unreal the size would probably double (at least) just in "un-used" stuff.
Thanks for commenting, they all deserve some credit for their games, a lot of hard work is put in to them! <3